Screw conveyor for the transport of goods hanging from hanger supports

ABSTRACT

A screw conveyor for the transport of, for example, pieces of clothing hanging on clothes hangers, comprises a screw shaft train ( 22 ) which may be rotated about the shaft axis ( 24 ) thereof, with a transport groove system ( 26 ), machined into the outer surface thereof along the shaft axis ( 24 ) in the form of a screw. The clothes hangers may be hung in the transport groove system ( 26 ), using the hanger hooks ( 20 ) thereof and axially transported by rotation of the screw shaft train ( 22 ). According to the invention, the transport groove system ( 26 ) comprises at least one primary transport groove ( 46, 48 ), from which a secondary transport groove ( 52, 54 ), preceding the primary transport groove ( 46, 48 ) in relation to the transport direction ( 16 ) of the goods for transport, branches at a branching position ( 62 ). The embodiment of the primary transport groove ( 46, 48 ) and the secondary transport groove ( 52, 54 ) is set, particularly with regard to the slope profile thereof, such that clothes hangers ( 12   a ) free of crossovers, which approach the branching position ( 62 ) in the primary transport groove ( 46, 48 ), pass the branching point ( 62 ) without leaving the primary transport groove ( 46, 48 ). A sensor arrangement ( 68 ) is provided on the screw shaft train ( 22 ) for recognition of clothes hangers ( 12   b   , 12   c ) with a cross-over, which is also embodied to monitor the secondary transport groove ( 52, 54 ) for clothes hangers ( 12   c ) transported therein.

The invention relates to a screw conveyor for transporting conveyablearticles hanging on hanging carriers.

Screw carriers are used, for example, for transporting items of clothinghung on clothes hangers, for example within the context of asuspension-type conveying installation for sorting and order-pickingitems of clothing. In the screw conveyor, the clothes hangers aresuspended, by way of their upper hanger hooks, in the helix or helicesof a screw shaft, the helix or helices being formed by a system ofconveying grooves. If the screw shaft is driven in rotation about itsshaft axis, then the clothes hangers guided in the conveying-groovesystem are advanced in the direction of the shaft axis.

It is often the case that, rather than being supplied to the screwconveyor completely separately from one another, the clothes hangers aresupplied in more or less disordered batches of bunched-up clotheshangers. This often results in two (or more) clothes hangers crossingover, i.e. in one clothes hanger which is suspended, by way of itshanger hook, in the conveying-groove system of the screw shaft upstreamof another clothes hanger—as seen in the conveying direction of theitems of clothing—passing, by way of its hanger crosspiece, behind thehanger crosspiece of this other, subsequent clothes hanger, with theresult that the two clothes hangers cross over at their hanger necks.

In order for it to be possible for the clothes hangers to be dischargedindividually from the screw conveyor, for example onto individual hangercarriers, crossed-over clothes hangers have to be disentangledbeforehand. Configurations of the conveying-groove system of the screwshaft which make it possible for such crossed-over clothes hangers to bedisentangled from the outside, without manual or mechanicalintervention, as they pass through the screw conveyor are known. In thiscase, the crossed-over clothes hangers are guided up to one another inthe conveying-groove system by way of their hanger hooks until, finally,one of the clothes hangers is disengaged from the other and is liftedbeyond the same, and the crossover is eliminated in this way. Inpractical usage, however, it has been found that it is not alwayspossible for all crossovers of clothes hangers to be reliably eliminatedin this way. In order, nevertheless to ensure that the clothes hangerscan leave the screw conveyor individually and without any crossovers, itwould then be necessary to give a member of operating staff the task ofconstantly observing the procedures in the screw conveyor andintervening if he/she detects any remaining crossovers of clotheshangers. Of course, this uses up operating staff and stands in the wayof the general wish for the conveying processes to be, as far aspossible, automated.

The object of the invention is thus to configure a screw conveyor suchthat it allows automated detection of crossed-over clothes hangers, orother hanging carriers used for transporting conveyable articles.

In order to achieve this object, the invention takes as its departurepoint a screw conveyor for transporting conveyable articles hanging onhanging carriers, in particular items of clothing hung on clotheshangers, comprising a screw-shaft line which can be rotated about itsshaft axis and has a conveying-groove system which is made in the outersurface of the screw-shaft line, winds helically along and around theshaft axis, and in which the hanging carriers can be suspended, by wayof carrying hooks, and can be conveyed axially by rotation of thescrew-shaft line.

It is proposed according to the invention, for such a screw conveyor,that the conveying-groove system has at least one primary conveyinggroove, from which a secondary conveying groove, which precedes theprimary conveying groove—as seen in the conveying direction of theconveyable articles along the shaft axis—branches off at a branching-offlocation, the configurations of the primary conveying groove and of thesecondary conveying groove being coordinated, in particular in respectof the pitch profile thereof, such that crossover-free hanging carrierswhich approach the branching-off location in the primary conveyinggroove pass the branching-off location without leaving the primaryconveying groove, and that, in order to detect crossed-over hangingcarriers, the screw-shaft line is assigned a sensor arrangement which isdesigned for monitoring at least the secondary conveying groove forhanging carriers conveyed therein.

The invention makes use of the fact that, in the case of crossed-overhanging carriers, which are guided—if appropriate once they have passedthrough an upstream separating section—in different turns of theconveying-groove system of the screw-shaft line, the carrying hooks ofthese hanging carriers are subjected to tensile forces which try to drawthe carrying hooks toward one another. This effect, which is equivalentto the tendency of the hanging carriers to compensate for theircrossover-induced oblique position, is caused merely by the weight ofthe hanging carriers, but is significantly enhanced by the weight of thearticles hanging on the hanging carriers. In the case of twocrossed-over hanging carriers, the carrying hook of the leading hangingcarrier, as seen in the conveying direction, is thus subjected to anaxially rearwardly directed tensile force, while the carrying hook ofthe trailing hanging carrier is subjected to an axially forwardlydirected tensile force. As a result, the leading hanging carrier (likeall the rest of the hanging carriers which are free of crossovers) doesnot leave the primary conveying groove at the branching-off location,but the trailing hanging carrier, on account of the tensile forcedriving it axially forward, enters into the secondary conveying grooveat the location at which the latter branches off from the primaryconveying groove. Consequently, the action of a hanging carrier runninginto the secondary conveying groove is a reliable indication of thepresence of crossed-over hanging carriers. In the case of the solutionaccording to the invention, the sensor arrangement allows such an eventto be detected automatically, and thus without any need for operatingstaff.

The sensor arrangement may comprise a first sensor, for monitoring thesecondary conveying groove, and a second sensor, which is arranged aheadof the first sensor, as seen in the conveying direction, and is intendedfor monitoring the primary conveying groove for hanging carriersconveyed therein, an evaluation unit, which is connected to bothsensors, emitting a crossover-detection signal when the two sensorsdetect a hanging carrier in the respective conveying groove in apredetermined time-specific relationship with respect to one another, inparticular simultaneously.

The secondary conveying groove expediently opens out into the primaryconveying groove again at a distance from the branching-off location. Inpractical usage, it has proven advantageous if the secondary conveyinggroove extends approximately over a complete turn between its locationat which it branches off from the primary conveying groove and itslocation at which it opens out into the primary conveying groove.

In order to increase the capacity of the screw conveyor, theconveying-groove system may have a plurality of at least two primaryconveying grooves which wind around the shaft axis one beside the other.A secondary conveying groove will preferably then branch off from eachof these primary conveying grooves, the sensor arrangement beingdesigned for monitoring each of the secondary conveying grooves forhanging carriers conveyed therein. It is possible here, upstream of thebranching-off locations of the secondary conveying grooves, for examplein a separating section, for one of the primary conveying grooves tostart between two successive turns of another primary conveying groove.This makes it possible to protect the screw conveyor against overloadingwherever the relevant primary conveying groove starts.

For reasons of cost and on account of the straightforward operation, itis recommended to use an inductive sensor arrangement for metallichanging carriers. Of course, this does not preclude the use of sensorarrangements which operate in accordance with other principles, forexample an optical sensor arrangement.

An exemplary embodiment of the invention is explained in more detailhereinbelow with reference to the attached drawings, in which:

FIG. 1 illustrates a highly schematic overall view of a screw conveyoraccording to the invention,

FIG. 2 illustrates an enlarged perspective view of a shaft portion ofthe screw-shaft line of the screw conveyor from FIG. 1,

FIG. 3 illustrates the shaft portion from FIG. 2 in a different rotaryposition,

FIG. 4 illustrates the shaft portion from FIG. 2 in yet another rotaryposition, and

FIG. 5 illustrates, schematically, a projected development of theconveying grooves which are made in the shaft portion from FIGS. 2 to 4.

The screw conveyor which is shown in FIG. 1, and is designated ingeneral terms there by 10, serves for transporting hanging carriers 12,which are supplied, and transferred to the screw conveyor 10, in anintroduction region 14 and, following transportation along a conveyingdirection 16, are discharged from the screw conveyor 10 in a dischargingregion 18. In the present example, the hanging carriers 12 are clotheshangers which each have a hanger hook 20 and have items of clothing (notillustrated specifically) hanging on them. It goes without saying thatthe screw conveyor 10 can also be used, in principle, for transportingany other desired hanging carriers instead of such clothes hangers. Thescrew conveyor is preferably used for receiving the clothes hangers 12from an upstream transporting system, for example a pawl-type conveyor,in the introduction region 14 and for transferring them to a downstreamtransporting system, for example a suspension-type conveying arrangementwith individual hanger carriers which can be displaced on rollers, inthe discharging region 18. In order to transport the clothes hangers 12in and out, it is, of course, also possible to use transporting systemsother than those mentioned above, for example a suspension-typeconveying arrangement with multiple hanger carriers which can bedisplaced on rollers, these often being referred to as trolleys andhaving a carrying bar on which a plurality of clothes hangers 12 can besuspended.

The screw conveyor has a screw-shaft line 22, which has its shaft axis24 arranged parallel to the conveying direction 16 and is mounted suchthat it can be rotated about this axis 24. A conveying-groove system 26is made in the circumferential casing of the screw-shaft line 22 andwinds along and around the shaft axis 24, it being possible for theclothes hangers 12 supplied to the screw conveyor 10 to be suspended, byway of their top hanger hooks 20, in said conveying-groove system. Theconveying-groove system 26 forms an arrangement of helices which servesfor guiding the clothes hangers 12. If the screw-shaft line 22 is madeto rotate about its shaft axis 24, then the clothes hangers 12 hangingthereon are advanced in the axial direction. The schematic drawing ofFIG. 1 illustrates the conveying-groove system 26 as though it wouldform just a single helix which extends with constant pitch over theentire length of the screw-shaft line 22. This illustration, however,serves merely to simplify matters; it goes without saying that theconveying-groove system 26 may form, at least in certain sections, aplurality of adjacent helices and it may be possible to vary the pitchof each helix along the shaft axis 24. By varying the helix pitch and/orthe number of helices, it is possible to achieve different effects. Forexample, the clothes hangers 12 may be separated by the turns of a helixbeing so close together that only a single clothes hanger can beaccommodated in each turn. The helix pitch here is reduced such that itis approximately equal to or even somewhat less than the wire thicknessof the hanger hooks 20. It is then possible for the turns to becomegradually further apart from one another again, that is to say for thepitch of the helix to increase again gradually. An increase in thenumber of helices, for example doubling from one helix to two helices,makes it possible to double, for example, the number of clothes hangers12 which can be transported. If such an additional helix is provided atcritical locations along the screw-shaft line 22, it may be possible toprevent the screw conveyor 10 from “overloading”.

A rotary-drive arrangement, which is designated in general terms by 28,serves for driving the screw-shaft line 22 in rotation. Thisrotary-drive arrangement 28 has at least one flexible drive belt 30,which is arranged preferably at an axial distance from the longitudinalends of the screw-shaft line 22, wraps around the screw-shaft line 22,over part of its circumferential casing, such that it transmits drivingpower, for example by means of interengaging toothing formations, and ismade to circulate in an endless loop by means of an electric drive motor32. In the present example of FIG. 1, two such drive belts 30 are shown.The two drive belts 30 each drive, independently of one another, one oftwo coaxial segments 34, 36 of the screw-shaft line 22, the segmentsbeing separated from one another at a separating location 38, which isindicated by dashed lines, and being rotatable about the shaft axis 24independently of one another. An electronic control unit 40 allows thedrive motors 32 to be controlled independently of one another, inparticular such that their speeds can be changed. Of course, it is alsopossible for the screw-shaft line 22 to be formed by a continuous,non-segmented screw shaft.

Each drive belt 30 has, on the outside of its loop, an arrangement ofparallel channels 42 which extend over the entire width of the relevantdrive belt 30 and run obliquely in relation to the direction in whichthe latter circulates. These channels 42 are designed, and oriented inrelation to the conveying-groove system 26 of the screw-shaft line 22,such that it is possible for clothes hangers 12 which approach one ofthe drive belts 30 to run directly into one of the channels 42 from theconveying-groove system 26 and, after crossing the relevant drive belt30, to be re-introduced into the conveying-groove system 26 of thescrew-shaft line 22. This makes it possible for the clothes hangers 12,as they pass through the screw conveyor 10, to be moved axially beyondall the drive belts 30 in a reliable manner, and with guidance.

In the case of a preferred usage form of the screw conveyor 10, theclothes hangers 12 can be supplied to the screw conveyor 10 indisordered groups of several clothes hangers in each case, the screwconveyor 10 having the task of conveying the clothes hangers 12,separating them, disentangling them, synchronizing them and countingthem, with the result that they leave the screw conveyor 10 individuallyone after the other. For this purpose, a first section of thescrew-shaft line 22, which follows the introduction region 14, isexpediently designed as an accumulating conveyor which, with the aid ofa switchable stop (not illustrated specifically in FIG. 1), allows theclothes hangers which are supplied to the screw-shaft line 22 toaccumulate. This accumulating section may be followed by a separatingsection and a disentangling section which, merely by an appropriateconfiguration of the conveying-groove system 26, effect separation ofthe clothes hangers 12 and at least partial disentanglement ofcrossed-over clothes hangers 12. Such separating and disentanglingsections are known per se in the case of screw conveyors. In the case ofthe clothes hangers 12 being supplied to the screw conveyor 10 inbatches and then building up, however, the clothes hangers 12 may getcaught up in one another such that only some of the crossovers of theclothes hangers 12 are eliminated in the disentangling section of thescrew-shaft line 22, and some clothes hangers 12 are still crossed overdownstream of the disentangling section. Since the followingtransporting processes would be disrupted to a considerable extent bythe screw conveyor 10 discharging crossed-over clothes hangers 12, thescrew-shaft line 22 is configured upstream of its discharging end, butdownstream of its disentangling section, with a crossover-recognitionsection, in which any remaining crossovers of clothes hangers 12 can bedetected.

The crossover-detection section mentioned is preferably formed on thesegment 34 of the screw-shaft line 22. The previously mentionedseparating and disentangling sections may likewise be formed on thesegment 34. The other segment 36, in contrast, can serve, at leastpredominantly, for accumulating the clothes hangers supplied to thescrew conveyor.

In order to explain the crossover-detection section of the screw-shaftline 22, reference is now made to FIGS. 2 to 4. These figures show ashaft portion 44 which, by way of its left-hand end in the figures,forms the discharging end of the screw-shaft line 22. On this shaftportion 44, the conveying-groove system 26 of the screw-shaft line 22has two primary conveying grooves 46, 48 which are intertwined, that isto say wind around the shaft axis 24 one beside the other, and arereferred to hereinbelow as main grooves. In order to show the coursetaken by the two main grooves 46, 48, the associated designations areindicated a number of times in FIGS. 2 to 4. As can be seen from FIG. 4in particular, the main groove 48 starts between two successive turns ofthe main groove 46. The approximate location at which the main groove 48starts is designated 50 in FIG. 4.

In the main groove 46, the clothes hangers 12 are conveyed onto theshaft portion 44. Even once they have passed through the above-mentionedseparating and disentangling sections of the screw-shaft line 22, thesituation where the clothes hangers 12, upon reaching the shaft portion44, are still partly bunched up, instead of being conveyed completelyseparately from one another in a respective groove turn, cannot be ruledout. The additional main groove 48 here has the purpose of assigningeach clothes hanger 12 supplied a dedicated groove turn, and thus ofpreventing overloading of the main groove 46. For this purpose, thecross section of the main groove 46 in the region upstream of thelocation 50 at which the main groove 48 originates is configured suchthat there is only space for a single clothes hanger 12 in each turn ofthe main groove 46. In addition, the turns of the main groove 46 in theregion upstream of the location 50 at which the main groove 48originates follow closely one after the other. As a result of thisconfiguration of the main groove 46, any surplus clothes hangers 12(surplus here means those clothes hangers 12 which exceed the conveyingcapacity of the main groove 46 and for which the main groove 46 thuscannot provide any turn in which to transport them) are forced outward,with the result that they are located approximately above the separatingrib between two successive turns of the main groove 46. If these surplusclothes hangers 12 then pass into the region of the location 50 at whichthe main groove 48 originates, they inevitably drop into the main groove48 and are transported further therein to the discharging end of theshaft portion 44.

Moreover, independently of the detection of crossed-over clotheshangers, we reserve the right to formulate independent protection forthe ideas explained above of allowing a second main groove to startbetween two successive turns of a first main groove.

Downstream of the location 50 at which the main groove 48 originates, asecondary conveying groove 52, 54, referred to hereinbelow as bypassgroove, branches off from each of the two main grooves 46, 48,respectively, and, following approximately one complete turn, runs intothe associated main groove again. The branching-off location at whichthe bypass groove 52 branches off from the main groove 46 can be seen inFIG. 3, and is designated 56 there. Beginning at this branching-offlocation 56 is a rib 58 which separates the main groove 46 from thebypass groove 52, and which winds around the shaft axis 24 as far as anopening-out location 60, at which the bypass groove 52 runs into themain groove 46 again. That location at which the bypass groove 54branches off from the main groove 48 can be seen in FIGS. 2 and 4, andis designated 62 there. Beginning at this branching-off location 62, ina corresponding manner, is a rib 64 which separates the main groove 48from the bypass groove 54, and which winds around the shaft axis 24 asfar as an opening-out location 66, at which the bypass groove 54 runsinto the main groove 48 again.

It can clearly be seen in FIGS. 2 to 4 that the bypass grooves 52, 54branch off forward, as seen in the conveying direction 16, from theirassociated main groove 46, 48, respectively, that is to say they precedethe latter, as seen in the conveying direction 16. In this case, themain groove 46 and the bypass groove 52, in the region of the branchinglocation 56 thereof, and the main groove 48 and the bypass groove 54, inthe region of the branching location 62 thereof, are configured, inrespect of their pitch and, if appropriate, also of their cross section,such that individually conveyed clothes hangers which are not crossedover other clothes hangers are transported further in the main groove 46or 48 when they approach the associated branching location 56, 62,respectively. In order to explain this situation, FIG. 2 depicts, by wayof example, an individual, crossover-free clothes hanger 12 a, which isconveyed in the main groove 48. When this clothes hanger 12 a approachesthe branching location 62, it passes the branching location 62 withoutleaving the main groove 48. The same applies, of course, to acrossover-free clothes hanger which is conveyed in the main groove 46.

The situation is different in the case of crossed-over clothes hangers.A pair of such crossed-over clothes hangers is depicted by way ofexample in FIG. 2; they are designated 12 b and 12 c there. A crossoverstate results when one clothes hanger has its hanger hook 20 engaging inan upstream turn of the conveying-groove system 26—as seen in theconveying direction 16—but has its hanger crosspiece, on which thetransported item or items of clothing hangs or hang, located behind thehanger crosspiece of another clothes hanger with its hanger hookengaging in a rear turn of the conveying-groove system 26. If such apair of crossed-over clothes hangers approaches the branching locationof the main groove 46 or 48, then the front clothes hanger, that is tosay the clothes hanger with the leading clothes hook 20, as seen in theconveying direction 16, passes the branching location without leavingthe relevant main groove. The reliability with which the front of twocrossed-over clothes hangers remains in the main groove, on account ofthe tensile action which is directed counter to the conveying direction16 and to which the hanger hook 20 of this clothes hanger is subjectedas a result of the crossover, is even greater than in the case ofindividual, crossover-free clothes hangers. The hanger hook 20 of thetrailing clothes hanger is likewise subjected to a tensile action,although the latter is directed in the conveying direction 16. Thisresults in the trailing clothes hanger being forced, at the branchinglocation, into the bypass groove which branches off from the respectivemain groove. This case is illustrated by the clothes hangers 12 b, 12 cdepicted in FIG. 2. The hanger hook 20 of the trailing clothes hanger 12c has run into the bypass groove 52. The leading clothes hanger 12 b inFIG. 2 is already located on the far side of the opening-out location 60(see FIG. 3), at which the bypass groove 52 meets up with the maingroove 46 again. In order to reach this location, however, it has notleft the main groove 46.

The presence of a clothes hanger in one of the bypass grooves 52, 54 isthus an indication of the presence of crossed-over clothes hangers. Aninductive sensor arrangement 68 serves for detecting such crossed-overclothes hangers. The sensor signals supplied by the sensor arrangement68 are evaluated by an electronic evaluation unit 70 and—if the latterestablishes the presence of crossed-over clothes hangers—are convertedinto a suitable reaction. This reaction may consist in the screwconveyor 10 being automatically switched off; as an alternative, or inaddition, the evaluation unit 70 may actuate an optical and/or acousticwarning device (not illustrated specifically).

The sensor arrangement 68 has two sensors 72, 74, which are spaced apartaxially from one another above the shaft portion 44. The position anddistance between the sensors 72, 74 are selected such that, in a rotaryposition of the shaft portion 44 in which one of the bypass grooves 52,54 runs past precisely beneath the rear sensor 72, as seen in theconveying direction 16—the main groove assigned to this bypass groove,at the same time, runs past precisely beneath the front sensor 74 by wayof its next-following turn in front. This can clearly be seen in FIG. 2.In that rotary position of the shaft portion 44 which is shown there,the rear sensor 72 is located precisely above the bypass groove 52,while the front sensor 74 is located precisely above the main groove 46,to be precise at a location of the main groove 46 which is situated someway downstream of the opening-out location 60. If, in the case of suchpositioning of the sensors 72, 74, a pair of crossed-over clotheshangers passes through the shaft portion 44, they reach the two sensors72, 74 simultaneously. The sensors 72, 74 thus simultaneously emit asensor signal to the evaluation unit 70, which then establishes thepresence of a crossover state. In the case of individual, crossover-freeclothes hangers, in contrast, it is always just one of the sensors 72,74 which emits a signal.

The relationships which have been explained above can easily beunderstood from the projected development of the main grooves 46, 48 andof the bypass grooves 52, 54 which is shown in FIG. 5.

1. A screw conveyor for transporting conveyable articles hanging onhanging carriers, in particular items of clothing hung on clotheshangers, comprising a screw-shaft line which can be rotated about itsshaft axis and has a conveying-groove system which is made in the outersurface of the screw-shaft line, winds helically along and around theshaft axis, and in which the hanging carriers can be suspended, by wayof carrying hooks, and can be conveyed axially by rotation of thescrew-shaft line, wherein the conveying-groove system has at least oneprimary conveying groove, from which a secondary conveying groove, whichprecedes the primary conveying groove, as seen in the conveyingdirection of the conveyable articles along the shaft axis, branches offat a branching-off location, the configurations of the primary conveyinggroove and of the secondary conveying groove being coordinated, inparticular in respect of the pitch profile thereof, such thatcrossover-free hanging carriers which approach the branching-offlocation in the primary conveying groove pass the branching-off locationwithout leaving the primary conveying groove, and wherein, in order todetect crossed-over hanging carriers, the screw-shaft line is assigned asensor arrangement which is designed for monitoring at least thesecondary conveying groove for hanging carriers conveyed therein.
 2. Thescrew conveyor as claimed in claim 1, wherein the sensor arrangementcomprises a first sensor, for monitoring the secondary conveying groove,and a second sensor, which is arranged ahead of the first sensor as seenin the conveying direction, and is intended for monitoring the primaryconveying groove for hanging carriers conveyed therein, and wherein anevaluation unit, which is connected to both sensors, emits acrossover-detection signal when the two sensors detect a hanging carrierin the respective conveying grooves in a predetermined time-specificrelationship with respect to one another, in particular simultaneously.3. The screw conveyor as claimed in claim 1, wherein the secondaryconveying groove opens out into the primary conveying groove again at adistance from the branching-off location.
 4. The screw conveyor asclaimed in claim 3, wherein the secondary conveying groove extendsapproximately over a complete turn between its location at which itbranches off from the primary conveying groove and its location at whichit opens out into the primary conveying groove.
 5. The screw conveyor asclaimed in claim 1, wherein the conveying-groove system has a pluralityof at least two primary conveying grooves which wind around the shaftaxis one beside the other and from each of which a secondary conveyinggroove branches off, the sensor arrangement being designed formonitoring each of the secondary conveying grooves for hanging carriersconveyed therein.
 6. The screw conveyor as claimed in claim 5, whereinupstream of the branching-off locations of the secondary conveyinggrooves, one of the primary conveying grooves starts between twosuccessive turns of another primary conveying groove, in particular in aseparating section of the screw-shaft line, in which the pitch of theother primary conveying groove is made to be approximately equal to orless than the material thickness of a carrying hook.
 7. The screwconveyor as claimed in claim 1, wherein the sensor arrangement isconfigured as an inductive sensor arrangement.